A typical color ink jet print head includes an array of ink jets that are closely spaced from one another for use in ejecting drops of ink toward a receiving surface. The typical print head also has at least four manifolds for receiving black, cyan, magenta and yellow ink for use in monochrome plus subtractive color printing. The number of such manifolds may be varied where a printer is designed to print solely in black ink, gray scale or with less than a full range of color.
In a conventional ink jet print head, each ink jet is paired with an electro mechanical transducer, such as a piezoelectric transducer (PZT). The transducer typically has metal film layers to which an electronic transducer driver is electrically connected. When a voltage is applied across the metal film layers of the transducer, the transducer attempts to change its dimensions. Because it is rigidly attached to a flexible diaphragm, the transducer bends and deforms the diaphragm, thereby causing the outward flow of ink through the ink jet.
Prolonged use of a PZT-driven ink jet print head at elevated temperatures can alter print head performance. This change in performance can result in image degradation due to the performance variations. For example, the drop mass of ejected ink drops can vary as the print head components are thermally conditioned over time. The positioning of the ejected ink drops on the receiving surface can also vary with thermal conditioning.
It is known to manually adjust the voltage applied to a PZT-driven ink jet to offset variations in ink drop mass. However, this manual voltage adjustment typically cannot be performed by an end-user, and requires a service professional to travel to the end-user site to perform the adjustment. This process is time-consuming and relatively expensive for the user. Additionally, for practical and economical reasons this manual adjustment procedure is performed only periodically. This reduces the effectiveness of the adjustment procedure in maintaining a consistent ink drop mass.
The present invention provides a method and apparatus for automatically compensating for thermal conditioning of an ink jet print head. Thermal conditioning of the print head is monitored and the voltage supplied to the ink jet transducer is adjusted over time to maintain a more consistent ink drop mass.